Vibratory tools are used to dislodge a stuck object known as a fish from a downhole location. They have other applications such as allowing a pulling force to be transmitted from the surface to a fish stuck in a deviated wellbore. In that application the vibratory devices can be placed in the deviation such that their presence helps transmit forces to the fish that would have otherwise been resisted by the deviated wellbore through which the string extended to reach the fish. An illustration of such as application is U.S. Pat. No. 6,502,638.
Vibratory tools known in the art have operated on a similar principle. An overpull is applied to the string supporting the tool and pressure is applied within the string. A piston then travels against the bias of a spring, in effect stretching the string while compressing the spring. At some point of travel, the force applied by the spring that acts on a valve member becomes higher than the pressure applied from above to that valve member. When this happens, there is relative movement that takes the valve member off a seat. The pressure that had been keeping the valve member on the seat up to that point is suddenly relieved as the valve member is biased off the seat by the rising spring force due to compression of the spring. Once the valve member is off the seat, the pressure acting on the piston that drove the mandrel down against the spring in the first place is suddenly relieved. Flow through the tool causes a sudden drop in the applied pressure causing the piston to snap back under the spring force and re-close the valve. At that point the cycle repeats. There are variations on this basic concept. Some designs employ a piston or opposed pistons that drive the mandrel in opposed directions.
There are other common features of known designs that limit their utility. Most earlier designs did not have a capability to have a central passageway clear so that a wireline could be run through the tool to determine conditions in the vicinity of the fish. Using those designs, the vibratory tool had to be removed to run a wireline or other tools down to the fish. Most all of these designs had the dump valve that relieved pressure located in the center of the tool preventing a clear run through the tool for a wireline or other tools. A few examples of such designs are U.S. Pat. Nos. 6,062,324 and 6,206,101.
More recently a drop in dart that incorporates the working components of the vibratory tool has been developed as shown in U.S. Pat. No. 6,866,104. This patent offered a solution to the need to have wireline access through the tool body and the dart could be retrieved after the vibration operation that commenced with the landing of the dart and application of pressure. While this design allowed for wireline access through the tool it also included additional compromises unique to the design of a dart that landed and sealed around a seat downhole. The main area of compromise was that the components of the vibratory tool had to be made to fit in the dart and the dart was limited in outside diameter so that it could fit into the receptacle in the tool body. Doing this required miniaturization of the vibratory tool key components which limited the power delivery of the generated vibrations from the tool. The use of smaller components also increased the effects of fatigue on the moving parts of the vibratory tool and there were also many components to the dart assembly making it fairly costly to build and maintain.
Other issues that affected reliable operation in the previous designs included a dump valve assembly that was pounded against a seat with each cycle resulting in rapid wear and potential loss of sealing contact. Another problem in the past had been the limited power delivery from the driving piston since its area was limited by the maximum available inside diameter in the tool housing. Many applications simply needed a higher power delivery to get the fish released.
A few other examples of known designs for vibratory tools are U.S. Pat. Nos. 6,474,421; 6,182,775; 6,164,393; 5,875,842 and 5,375,671.
What is needed and is addressed by the tool described below is a collection of features that solve the issues with prior design and lead to a more economical and reliable design. The dump valve is reconfigured into an annular shape to keep the middle of the tool free and clear. This allows a central passage to exist to permit a wireline operation through the tool when the tool is not set up to be in vibratory mode. The tool can be simply put in vibratory mode by dropping a removable plug onto a seat. The dump valve opens and closes without getting slammed against a seat. The mandrel is powered by stacked pistons in the tool body to magnify the delivered power from the vibratory tool. Since the essential parts of the vibratory tool are in the housing and only the delivery of the plug is required to initiate operations, the remaining components can be designed to be more beefy so as to run longer and more reliably as compared to the prior design where the key movable components were delivered into the tool housing on a dart. The tool can be configured so that the pistons can travel their entire stroke without being banged against travel stops. The tool has the capability to tolerate continued downward mandrel movement to dissipate its momentum even after the dump valve opens. The components are then configured to apply power to the mandrel for a down cycle when the dump valve closes close to the point where the pistons reach their upward travel limit. In this way a longer power stroke is achieved in an effort to free the fish. The tool can be run to apply up oscillating forces with or without impacts depending on how the tool is operated by rig personnel. These and other advantages of the present invention and its scope will become more apparent to those skilled in the art from a review of the description of the preferred embodiment, the drawings and the claims appended below.